Over the last decade we have gained a detailed understanding of the static geochemical characteristics of arsenic and manganese contaminated aquifers and have characterized the rapid response of sediment to artificial chemical perturbations in incubation experiments. However, remarkably little is known about the basic aspects of hydrogeology that are vital for understanding the evolution of groundwater chemistry along flow paths that are contaminated by these metals. We do not know how the solute fluxes that drive manganese and arsenic mobility enter the aquifer, what patterns groundwater flow follows, or how solutes mix across different flow paths. Little is known about deeper groundwater flow, and basic issues such as the significance of regional flow and groundwater pumping are still controversial. In the proposed research, we will combine networks of sensors and geophysical imaging techniques with three-dimensional groundwater flow and transport models to characterized changing subsurface conditions. We will observe how subsurface conditions may be altered by installation of community supply wells, the most common approach to providing safe water, and we will develop predictive models for future shifts in groundwater chemistry. Our results will provide insight into the processes that cause metal mobilization from sediments, and will enable better management of contaminated groundwater.